Recent data continue to indicate that use of the insecticide DDT may have adverse effects on human health, but essentially no findings on this topic have been replicated, so the question is still open. Whether DDT has adverse effects is important because DDT is still used for malaria control in about 12 countries, and current recommendations by the World Health Organization that support DDT use are based on the assumption that it has basically no adverse health consequences for humans. DDE is the major metabolite of DDT and is a long-term biomarker of exposure. Experiments in animals indicate that DDE blocks androgen action and that exposure before birth can have devastating effects on male reproduction. In addition, two previous human studies suggest that higher exposure to DDE is associated with a shortended duration of lactation. Breast feeding prevents infant death. Therefore, DDT use may have the effect of increasing infant death. Furthermore, recent data suggest that DDT/DDE may cause pregnancy loss in humans. Additional information about these potential adverse effect are needed. Mexico used the insecticide DDT for malaria control until 1999; many people there in tropical areas have elevated blood levels of the DDT metabolite, DDE. My project in Mexico has two phases; both are based on the same group of subjects. I conducted phase 1 of this study: 1) To examine the relation between maternal serum levels of DDE in relation to evidence of decreased androgen action in 781 newborn males in Tapachula, Mexico. All phase 1 subjects were enrolled in 2002-2003; the response rate was 95%. Laboratory results on DDE levels became available this fiscal year. Phase 2 of this study began at the beginning of FY 2004. This study is following the women and children enrolled in Phase 1, to determine if DDT exposure is related to reduced length of lactation among mothers. In addition, the offspring will be followed to examine early-life DDT exposure in relation to infection and growth. Furthermore, preliminary analyses of our data from Mexico show that previous fetal loss was greater among women with higher DDE levels. Last year's progress Analysis of the anthropometric data shows that the measurements were done reliably and that the measurement error was relatively small compared with the true variation among subjects. A manuscript reporting this is nearly ready for submission. Preliminary analyses show no relation of DDE exposure with measures of androgenization in newborn males. For phase 2, to date, 757 subjects have been followed-up; their breastfeeding duration and status has been ascertained, and the child's growth and infection disease history ascertained. Follow-up of the subjects has been completed for 87% of eligible subjects, and will end 9-30-05. Preliminary analyses of the data show no relation of DDE with length of lactation.